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(11) | EP 0 706 286 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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Color printer calibration correcting for local printer non-linearities Farbdruckerabgleich zur Verbesserung lokaler Druckunregelmässigkeiten Calibrage d'imprimante de couleurs pour corriger des irrégularitées locales d'imprimante |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention is directed towards compiling look up tables representative of printer characteristics, to enable the conversion of colors defined in a first color space to colors defined in the printer color space, and more particularly to a method of making such table more linear.
[0002] The generation of color documents can be thought of as a two step process: first, the generation of the image by means of scanning an original document with a color image input terminal or scanner or, alternatively, creating a color image on a work station operated in accordance with a color image creation program; and secondly, printing of that image with a color printer in accordance with the colors defined by the scanner or computer generated image. Scanner output is commonly transformed to a color space of tristimulus values, i.e., RGB (red-green-blue). Commonly, these values are a linear transformation of the standard XYZ coordinates of CIE color space, or a corrected transform of those values. In the case of computer generated images, colors defined by the user at the user interface of a workstation can be defined initially in color space of tristimulus values. These colors are defined independently of any particular device, and accordingly reference is made to the information as being "device independent".
[0003] Printers often have an output which can be defined as existing in a color space called CMYK (cyan-magenta-yellow-key or black) which is uniquely defined for the printer by its capabilities and colorants. Printers operate by the addition of multiple layers of ink or colorant in layers to a page. The response of the printer tends to be relatively non-linear. These colors are defined for a particular device, and accordingly reference is made to the information as being "device dependent". Thus, while a printer receives information in a device independent color space, it must convert that information to print in a device dependent color space, which reflects the gamut or possible range of colors of the printer.
[0004] The desirability of operating in a device independent color space with subsequent conversion to a device dependent color space is well known, as shown by US-A 4,500,919 to Schreiber and US-A 2,790,844 to Neugebauer, and US-A 4,275,413 to Sakamoto. There are many methods of conversion between color spaces, all of which begin with the measurement of printer response to certain input values. Commonly, a printer is driven with a set of input values reflecting color samples throughout the printer gamut, the color samples are printed in normal operation of the printer. As previously noted, most printers have non-linear response characteristics.
[0005] In US-A 4,275,413 to Sakamoto, the information derived is placed into lookup tables, stored in a memory, perhaps ROM memory or RAM memory where the lookup table relates input color space to output color space. The lookup table is commonly a three dimensional table since color is defined with three variables. In RGB space, at a scanner or computer, space can be defined as three dimensional with black at the origin of a three dimensional coordinate system 0,0,0, and white at the maximum of a three dimensional coordinate system which an 8-bit system, would be located at 255, 255, 255. Each of the three axes radiating from the origin point therefore respectively define red, green, and blue. A similar construct can be made for the printer, with axes representing cyan, magenta, and yellow. In the 8-bit system suggested, there will be, however, over 16 million possible colors (2563). There are clearly too many values for a 1:1 mapping of RGB to CMY. Accordingly, as proposed in US-A 4,275,413 to Sakamoto, only a relatively small number of samples are used to do the mapping from RGB to CMY, perhaps on the order of 1,000. Therefore, the lookup tables consist of a set of values which could be said to be the intersections for corners of a set of cubes mounted on top of one another. Colors falling within each cubic volume can be interpolated from the measured values, through many methods including tri-linear interpolation, tetrahedral interpolation, polynomial interpolation, linear interpolation, and any other interpolation method depending on the desired speed and accuracy of the result.
[0006] It would be very easy to index device dependent color values or specifications to device independent color specifications, but that is not the requirement. Instead, device independent specifications must be mapped to device dependent specifications. Several problems arise. Of course, the primary problem is that the printer response is not a linear response. A second problem is that the color space, and therefore the coordinates defined in the color space must be maintained as a uniform grid, for maximum efficiency of some interpolation methods, particularly for tetrahedral interpolation, a very desirable method of interpolation.
[0007] Accordingly, a three dimensional look up table (LUT) may be constructed which puts device independent input values into a predictable grid pattern. One method of accomplishing this requirement is by an interpolation process which derives a value at a desired location as a function of all (or a significant set) of measured color values. One way of doing this is to use Shepard's Method (see, for example "Shepard's Method of 'Metric Interpolation' to Bivariate and Multivariate Interpolation" by W. Gordon and J. Wixom, Mathematics of Computation, Vol. 32, No. 141, January 1978, pp. 253-264). Shepard's Method suggests that a vector can be thought of as defining the difference between an asked-for color which was directed to a printer in the printed color. Then, for any other point in color space which is desired, that point can be thought of as a vector quantity, derived by averaging over the space all the vectors, each vector weighted by a function which decreases its effect on the vector as that vector is further and further away from the point coloring question. In one useful formula, each vector is weighted by a function of 1/d 4.
[0008] Alternatively the method of Po-Chieh Hung, "Colorimetric Calibration for Scanners and Media", SPIE, Vol. 1448, Camera and Input Scanner System, (1991), describes a method of inverse tetrahedral interpolation, to the same effect as the described Shepard's Method (see also US-A 5,296,923 to Hung). A requirement of this method is that the color space be segmented into a set of non-overlapping, space-filling tetrahedrons. This segmentation requirement is fulfilled by using only data from a full rectangular array of points, where it is easy to define the mesh of points which define the tetrahedrons.
[0009] A problem encountered in the calibration process is that of having most colors being reproduced successfully, but having a few regions of color space that are not well behaved in terms of the empirically derived calibration model. The addition of a few more calibration points in these poorly behaved areas, would appear to be a solution to the problem. However, because inverse tetrahedral interpolation requires a full rectangular grid of data points, to obtain the "few more calibration points" in the poorly behaved areas really requires the addition of hundreds of more calibration points. Figure 1 illustrates the problem in two dimensions for simplicity, where a, b, c and d represent colors which reproduce successfully in a color space transformation, while point e does not. Adding points Pi, as in Figure 1A presumably would resolve the reproduction problem, but that arrangement does not provide a color space which is readily segmentable into a set of non-overlapping, space-filling tetrahedrons. This segmentation requirement is fulfilled by using only data from a full rectangular array of points.
[0010] It is an object of the invention to provide a calibration method providing additional data points to support inverse tetrahedral interpolation for the derivation of color space transformation look up tables, without substantially increasing the amount of empirically measured data.
[0011] In accordance with one aspect of the invention, which in its broadest aspects is defined in claims 1, 4 and 7, the color printer calibration method for improving printer accuracy in regions of local non-linearity includes the steps of: a) starting with filled rectangular array of color mappings A0 mapping printer signals to device independent color space signals; b) empirically deriving a set of color mappings Pi in an area of interest; c) using a set of planes defined by the color mappings of A0, and the set of empirically derived color mappings Pi, identifying a new set of planes such that each point defined by A0 and each point defined by Pi is located at the intersection of three planes, the intersection points of this expanded number of planes defining a set of points Pi(expanded) that define a full rectangular array A1 of mappings including mappings A0, mappings Pi and mappings Pi(expanded); d) storing said mapping A1 for use in the creation of a new color space transformation LUT for use with said printer.
[0012] In accordance with another aspect of the invention, the method includes, before step d), the step of substituting into mapping A1, any empirically derived mappings from A0 and any empirically derived mappings from Pi.
[0013] In accordance with yet another aspect of the invention, the method includes, before step d), the step of replacing mappings in A1 that are defined by points from mapping A0 and near a value of mapping Pi, with new mapping values which take into account the nearby Pi mappings.
[0014] In using the described method, the goal of obtaining a filled rectangular or three dimensional mapping is obtained, while additionally improving calibration results through the use of the new empirical data to describe color mapping adjacent to the new empirical points.
[0015] These and other aspects of the invention will become apparent from the following descriptions to illustrate a preferred embodiment of the invention read in conjunction with the accompanying drawings in which:
Figures 1A and 1B show the problem addressed by the present invention in a two dimensional example;
Figures 2 and 3 together illustrate an overall system block diagram showing a color printing system in which the present invention might find use;
Figure 4 shows the principle of the present invention, whereby after derivation of new empirical values, a new filled rectangular array must be generated; and
Figure 5 illustrates the construction of the new color calibration mapping using the method and system described herein.
[0016] Referring now to the drawings, a basic system for carrying out the present invention is shown in Figure 2. The system includes a scanner 10, such as perhaps the color scanner available in the Xerox 5775 digital color copiers, which can be calibrated to produce a set of digital colorimetric or device independent data describing a scanned image 12, which, by definition can be defined in terms of the colorimetric Ro,Go,Bo space. Resulting from the scanning operation is a set of scanner image signals Rs, Gs, Bs, defined in device dependent scanner terms. Incorporated into the scanner or another processing path is a post-scanning processor 14, which provides correction of scanner image signals Rs, Gs, Bs to colorimetric terms, Rc, Gc, Bc, typically digital in nature. The values may be in terms of CIE color space (r,g,b), or the L*a*b* luminance-chrominance space (LC1C2). A color space transform, indicated by block 20, such as that described in US-A 4,275,413 to Sakamoto, is used to convert the device independent data to device dependent data. The output of color space transform 20 is the image defined in terms of a device dependent space, or colorant driving signal Cp, Mp, Yp, Kp that will be used to drive a printer 30. In one possible example, the colorant values represent the relative amounts of cyan, magenta, yellow, and black toners that are to be deposited over a given area in an electrophotographic printer, such as, again, Xerox 5775 digital color copiers. The printed output image may be said to be defined in terms of Rp,Gp,Bp, which are hoped to have a relationship with Ro,Go,Bo such that the printed output image has a color that is colorimetrically similar to the original image, although that similarity is ultimately dependent upon the gamut of the printing device. Black addition for under color removal and gray balance processing may also be combined into the color space transform element. Although these features are not required, they are desirable and are illustrated herein. When we refer to colorimetric spaces, we are referring to spaces which are transforms of CIE XYZ space (1931). Such colorimetric spaces are also inherently device independent. When we refer to device dependent space, we refer to a color space which is defined only in terms of operation of the device using it. While many color spaces have three dimensions, it is possible to have color spaces with less than three dimensions or more than three dimensions.
[0017] With reference now to Figure 3, and color space transformation and color correction 20, initially, Rc, Gc, Bc color signals are directed to an interpolation device 140, which includes a three dimensional lookup table stored in a device memory 150 such as a RAM or other addressable memory device, which will meet speed and memory requirements for a particular device. Color signals Rc, Gc, Bc are processed to generate address entries to the table which stores a set of transform coefficients with which the Rc, Gc, Bc may be processed to convert them to Cx, Mx, Yx colorant signals or any multi-dimensional output color space including but not limited to CMYK or spectral data. Values which are not mapped may be determined through interpolation.
[0018] It will no doubt be recognized that there are many methods of providing a transform from device independent data to device dependent data, with US-A 4,275,413 to Sakamoto describing one method, which itself can be varied. Once a conversion table is established, a method of interpolation referred to as tri-linear or cubic interpolation may also be used to calculate output values from the limited set of input values.
[0019] To create the table, a set of color patches are created, preferably including determined linearization and black addition. This is done by printing and measuring about 1000 to 4000 patches of printer colors distributed throughout the color space, i.e., a large set of printer driving signals are generated, in varying densities of combinations of C,M,Y,K, and used to drive the printer. The color of each patch is measured, using a spectrophotometer to determine color in terms of Rc,Bc,Gc. The measured colors of these patches are used to build a three dimensional lookup table (LUT) relating Rc,Bc,Gc defined colors to CxMxYx defined colors. Conversions that do not include mapped and measured points may be interpolated or extrapolated.
[0020] With reference again to Figure 2, a calibration image is conveniently stored in a device memory such as calibration ROM 60, RAM, floppy or the like, or are generated on the fly with a predetermined generation function. Signals stored therein are directed to the printer under the control of printer controller 65. Spectrophotometer 70 (which can alternatively be a colorimeter, a calibrated densitometer or even a calibrated color scanner) is used to scan the calibration target and produce RoGoBo signal values as a function of sensed density, representing the colors of each scanned patch. Interpatch correlation processor 80 reads the responses provided from spectrophotometer 70 for each location in the calibration target and correlates the response with the input CMY signals, so that an RcGcBc to CMY mapping is generated. The data derived at interpatch correlation processor 80 is directed to LUT processor 100, which generates the required lookup tables for storage in color space transform and color correction 20.
[0021] Now the principle of the present invention will be described with reference to Figure 1A, 1B and Figure 4. Figure 1A is a two dimensional color space example chosen to simplify the more common problem in three dimensions. Figure 1A illustrates the required regular array of data values A0 with example mappings indicated by X's at points a, b, c and d. The problem is that printing a color corresponding to mapping O at point e is desired, but when that mapping is interpolated using existing data, it does not provide the expected color. If the surrounding mappings at points a(3,3), b(3,2), c(4,2) and d(4,3) are correct or acceptable, it may be concluded that the response of the system in this region of color space is very non-linear, and that linear interpolation from existing data will produce errors in the output. An improved characterization of the system response is required.
[0022] To obtain a better characterization of the printing system in this region, three more color patches are generated (a set referred to as Pi), generally within the limits of the region, and the printer response is measured, as indicated by the hollow squares in Figure 1B. The new patches Pi are located at (x,y) = (3.5, 2) (3.5, 2.75) and (4, 2.5). The actual locations and number of these patches can vary.
[0023] The newly derived mappings Pi cannot simply be added to the calibration set, because they will create situations where the region would not be divisible into non-overlapping space filling triangles (or tetrahedrons in the 3-D case). In the original data set A0, two non-overlapping space filling triangles in this region were formed by the points [(3,2), (4,2), (4,3)] and [(3,3), (3,2), (4,3)].
[0024] The inventive solution, illustrated in Figure 4, divides the region defined by these points into sets of smaller squares using linear interpolation and weighted averaging to estimate required values. This works in the 2-D case described here, but to maintain continuity across the boundary in the third dimension it is also necessary to add in an entire line (or plane, in the 3-D case) of new data points. That is, we must have a value at x = 3.5 for every possible Y value, and we must have a value at y = 2.5 and y = 2.75 for every possible X value. The set of new points (Pi (expanded)) which we must calculate are shown as solid squares in Figure 4. Initially, these values are based on the set of mappings A0.
[0025] Note that this process has the effect of maintaining a full and filled rectangular array of points, even though only a few new points on each line (or plane) were measured. The points on the line (or plane) which were not measured are obtained by linear interpolation. This is the same type of interpolation that would have been done later in the use of the data set, and is done in regions where we have not seen a problem with assuming a linear response of the system.
[0026] In addition to adding new data points by linear interpolation, the points which are "near" the new set of measured points (for example; the three points indicated by black squares at (x,y) = (3.5, 2.5), (3.5, 3.0), and (4.0, 2.75) in Figure 1B and Figure 4) are updated by a weighted averaging technique, such as Shepard's Method using data from Pi in addition to data from A0. Now, the three points at (3.5, 2.5), (3.5, 3.0), and (4.0, 2.75) in Figure 4 will be interpolated or evaluated using the values of (x,y) = (3.5, 2), (3.5, 2.75), (4, 2.5) from the set Pi, and the values at (x,y) = (4,2), and (4,3) from the set A0. It is believed that using these closer points would produce improved printer signals.
[0027] These newly derived mappings, which map regular printer signals to empirically derived colorimetric or device independent signals, are used initially in an inverse tetrahedral interpolation process, to produce a mapping of regular colorimetric signals to printer signals. This mapping is then loaded and used, for example to interpolate printer signals to produce an improved response for the color represented by the open circle of Figure 4.
[0028] The inventive method of improving printer linearity suggests that: given a filled rectangular array of points A0 mapping printer signals to device independent or colorimetric color space signals, it is desirable to add some set of points Pi, were i = 1, 2 . . . N, in such a way that a filled rectangular array of points is derived. This requirement is accomplished in four steps:
1) Identify a set of planes such that each new point Pi, and each original point defined by A0 will be located at the intersection of three planes in color space;
2) Using the set of points A0 as a starting condition, interpolate a new set of points A1, such that each 3 way intersection of the planes found in step 1) has an associated mapping. Initially, all values of A1 are based on values of A0.
3) Any points in A1 which also have measured values defined by an Ao or a Pi are updated to the correct (i.e., measured, not interpolated) values of Ao or Pi.
4) Any points in A1, which are not part of A0 or defined by a value Pi, but are near a value of Pi, are modified using nearby points in either A0 or Pi with Shepard's interpolation, or some other interpolation method. In the example above, any interpolated points contained within or in the box defined by (x, y) = (3,2) and (4,3) are updated using the three new points and the original values at the corners of the box.
[0029] Figure 5 illustrates the data flow in the system to accomplish the goals of the invention. The color space mappings forming mapping set A0 (the flawed mapping) will be used as the basis for creating the new mapping set A1 (the corrected mapping). Mappings Pi are generated in a standard manner, but are concentrated in color space in the region where any non-linearity was noted. The Pi mappings (there may be one, or any number required to represent the non-linearity) are directed from interpatch correlation 80, to data expander 200, which can conveniently be a function within LUT processor 100, to produce from the Pi values a set of Pi(expanded) mappings, including the Pi mappings and all the mappings required to fill the array based on the addition of the Pi mappings. The Pi(expanded) mappings are entered into the mapping set A1.
[0030] There is likely to be overlap between the A0 and Pi(expanded) mappings. That overlap can be handled in a two step process: 1) wherever there is an empirically derived mapping of Pi, such empirically derived mapping is substituted in A1 instead of A0, and 2) in regions closely adjacent in space to any of the new empirically derived mappings, the interpolated values are modified using the Pi mappings and the A0 mappings. Points are deemed to be closely adjacent if they fall within a rectangle (or a box in 3-D space) which also contains a new empirically derived mapping. Thus, arbitrator 202 operates on Pi and A0 to arbitrate the data which is loaded. Interpolator 204 operates using Pi and A0 as required by arbitrator 202, to generate new interpolated data for points near the new empirically derived mappings. These functions can be accomplished within function within LUT processor 100.
[0031] The new mappings are directed to LUT processor 100, in order to generate a new color transformation LUT for storage at color space transform and color correction 20.
[0032] It will be appreciated that while we have shown the use of the invention in the conversion of a device independent color space to a device dependent color space, the invention applies equally as well to conversions to any transformation from a first space to a second, device independent or device dependent.
a) empirically generating a second color mapping set Pi, mapping printer signals to colorimetric signals, said second color mapping set Pi being smaller than the first color mapping set A0 and overlapping a portion of the printer gamut therewith;
b) using said second color mapping set Pi and a first set of planes corresponding to the first color mapping set A0, identifying an expanded set of planes in which each mapping in the first color mapping set A0 and each mapping in said second color mapping set Pi are defined by points located at an intersection of three planes, the intersecting points of the expanded number of planes defining a set of points Pi(expanded) corresponding to a third color mapping set Pi(expanded);
c) generating a full rectangular array of color mappings defined by color mapping set A1, from the first color set mapping A0, said second color set mappings Pi and said third color mapping set Pi(expanded);
d) generating a new calibration for said printing system derived from said color mappings A1.
a) means for empirically generating a second color mapping set Pi, mapping printer signals to colorimetric signals, said second color mapping set Pi being smaller than the first color mapping set A0 and overlapping a portion of the printer gamut therewith;
b) means for using said second color mapping set Pi and a first set of planes corresponding to the first color mapping set A0, identifying an expanded set of planes in which each mapping in the first color mapping set A0 and each mapping in said second color mapping set Pi are defined by points located at an intersection of three planes, the intersecting points of the expanded number of planes defining a set of points Pi(expanded) corresponding to a third color mapping set Pi(expanded);
c) means for generating a full rectangular array of color mappings defined by color mapping set A1, from the first color set mapping A0, said second color set mappings Pi and said third color mapping set Pi(expanded);
d) means for generating a new calibration for said printing system derived from said color mappings A1.
a) directing a correction set of printer signals to said printing system to print a set of color patches with colorants on a medium corresponding to a color space region of non-linearity;
b) measuring colorimetric response of said printer in said color space region of non-linearity from said set of color patches and generating colorimetric response signals indicative thereof;
c) generating a second color mapping set Pi, mapping the correction set of printer signals to colorimetric response signals, said second color mapping set Pi being smaller than the first color mapping set A0 and overlapping a portion of the printer gamut therewith;
d) using said second color mapping set Pi and a first set of planes corresponding to the first color mapping set A0, identifying an expanded set of planes in which each mapping in the first color mapping set A0 and each mapping in said second color mapping set Pi are defined by points located at an intersection of three planes, the intersecting points of the expanded number of planes defining a set of points Pi(expanded) corresponding to a third color mapping set Pi(expanded);
e) generating a full rectangular array of color mappings defined by color mapping set A1, from the first color set mapping A0, said second color set mappings Pi and said third color mapping set Pi(expanded);
f) applying an inverse interpolation process to said color mapping set A1 to derive a new mapping of colorimetric response signals to printer signals, addressable by said colorimetric response signals, thereby generating a new calibration for said printing system.
a) empirisch einen zweiten Farbabbildungssatz Pi zu erzeugen, Druckersignale auf kolorimetrische Signale abzubilden, wobei der zweite Farbabbildungssatz Pi kleiner als der erste Farbabbildungssatz A0 ist und Überlappen eines Bereiches des Farbtonumfangs des Druckers damit;
b) Verwenden des zweiten Farbabbildungssatzes Pi und eines ersten Satzes von Ebenen, der dem ersten Farbabbildungssatz A0 entspricht, Erkennen eines erweiterten Satzes von Ebenen, in denen jede Abbildung in dem ersten Farbabbildungssatz A0 und jede Abbildung in dem zweiten Farbabbildungssatz P; durch Punkte definiert sind, die sich an Schnittpunkten von drei Ebenen befinden, wobei die Schnittpunkte der erweiterten Anzahl Ebenen einen Satz von Punkten Pi (erweitert) definieren, der einem dritten Farbabbildungssatz Pi(erweitert) entspricht;
c) Erzeugen einer vollen, rechteckigen Anordnung von Farbabbildungen, die durch einen Farbabbildungssatz A1 definiert sind, aus dem ersten Farbabbildungssatz A0, dem zweiten Farbabbildungssatz Pj und dem dritten Farbabbildungssatz Pi(erweitert);
d) Erzeugen einer neuen Kalibrierung für das Drucksystem, die von den Farbabbildungen A1 abgeleitet wird.
a) eine Einrichtung, zum empirischen Erzeugen eines zweiten Farbabbildungssatzes Pi und zum Abbilden von Druckersignalen auf kolorimetrische Signale, wobei der zweite Farbabbildungssatz Pi kleiner als der erste Farbabbildungssatz A0 ist und Überlappen eines Bereiches des Farbtonumfangs des Druckers damit;
b) eine Einrichtung zum Verwenden des zweiten Farbabbildungssatzes Pi und eines ersten Satzes von Ebenen, der dem ersten Farbabbildungssatz A0 entspricht, Erkennen eines erweiterten Satzes von Ebenen, in denen jede Abbildung in dem ersten Farbabbildungssatz A0 und jede Abbildung in dem zweiten Farbabbildungssatz Pi durch Punkte definiert sind, die sich an Schnittpunkten von drei Ebenen befinden, wobei die Schnittpunkte der erweiterten Anzahl Ebenen einen Satz von Punkten Pi (erweitert) definieren, der einem dritten Farbabbildungssatz Pi (erweitert) entspricht;
c) eine Einrichtung zum Erzeugen einer vollen, rechteckigen Anordnung von Farbabbildungen, die durch einen Farbabbildungssatz A1 definiert sind, aus dem ersten Farbabbildungssatz A0, dem zweiten Farbabbildungssatz Pi und dem dritten Farbabbildungssatz Pi (erweitert);
d) eine Einrichtung zum Erzeugen einer neuen Kalibrierung für das Drucksystem, die von den Farbabbildungen A1 abgeleitet wird.
a) einen Korrektursatz von Druckersignalen zu dem Drucksystem zu lenken, um einen Satz Farbflecken mit Farbmitteln auf einem Medium zu drucken, der einem Farbraumbereich mit Nichtlinearität entspricht;
b) Messen des kolorimetrischen Ansprechens des Druckers in dem Farbraumbereich mit Nichtlinearität durch den Satz Farbflecken und Erzeugen kolorimetrischer Ansprechsignale, die dies angeben;
c) Erzeugen eines zweiten Farbabbildungssatzes Pi, Abbilden des Korrektursatzes von Druckersignalen auf kolorimetrische Signale, wobei der zweite Farbabbildungssatz Pi kleiner als der erste Farbabbildungssatz A0 ist, und Überlappen eines Bereiches des Farbtonumfangs des Druckers damit;
d) Verwenden des zweiten Farbabbildungssatzes Pi und eines ersten Satzes von Ebenen, der dem ersten Farbabbildungssatz A0 entspricht, Erkennen eines erweiterten Satzes von Ebenen, in denen jede Abbildung in dem ersten Farbabbildungssatz A0 und jede Abbildung in dem zweiten Farbabbildungssatz Pi durch Punkte definiert sind, die sich an Schnittpunkten von drei Ebenen befinden, wobei die Schnittpunkte der erweiterten Anzahl Ebenen einen Satz von Punkten Pi (eiweitert) definieren, der einem dritten Farbabbildungssatz Pi (erweitert) entspricht;
e) Erzeugen einer vollen, rechteckigen Anordnung von Farbabbildungen, die durch einen Farbabbildungssatz A1 definiert sind, aus dem ersten Farbabbildungssatz A0, dem zweiten Farbabbildungssatz Pi und dem dritten Farbabbildungssatz Pi(erweitert);
f) Anwenden eines umgekehrten Interpolationsverfahrens auf den Farbabbildungssatz A1, um eine neue Abbildung von kolorimetrischen Ansprechsignalen an die Druckersignale abzuleiten, die durch die kolorimetrischen Ansprechsignale adressierbar sind, wodurch eine neue Kalibrierung des Drucksystem erzeugt wird.
a) génération empirique d'un second ensemble de mises en correspondance de couleurs Pj, mettant en correspondance des signaux d'imprimante et des signaux colorimétriques, ledit ensemble de mises en correspondance de couleurs Pj étant plus petit que le premier ensemble de mises en correspondance de couleurs A0 et se trouvant en chevauchement avec celles-ci sur une partie de la gamme de l'imprimante ;
b) d'utilisation dudit second ensemble de mises en correspondance de couleurs Pj et d'une premier ensemble de plans correspondant au premier ensemble de mises en correspondance de couleurs A0 identifiant un ensemble agrandi de plans dans lequel chaque mise en correspondance dans le premier ensemble de mises en correspondance de couleurs A0 et chaque mise en correspondance dans ledit second ensemble de mises en correspondance de couleurs Pj sont définis par des points situés à une intersection de trois plans, les points d'intersection du nombre agrandi de plans définissant un ensemble de points Pi(agrandis) correspondant à un troisième ensemble de mises en correspondance de couleurs Pi(agrandis) ;
c) de génération d'une matrice rectangulaire remplie de mises en correspondance de couleurs définie par un ensemble de mises en correspondance de couleurs A1, dérivé de la première mise en correspondance d'ensembles de couleurs A0, lesdites secondes mises en correspondance d'ensembles de couleurs Pj et ledit troisième ensemble de mises en correspondance de couleurs Pi(agrandi) ;
d) de génération d'un nouveau étalonnage pour ledit système d'impression dérivé desdites mises en correspondance de couleurs A1.
a) un moyen pour générer empiriquement un second ensemble de mises en correspondance de couleurs Pj, mettre en correspondance des signaux d'imprimante et des signaux colorimétriques, ledit second ensemble de mises en correspondance de couleurs Pj étant plus petit que le premier ensemble de mises en correspondance de couleurs A0 et se trouvant en chevauchement avec celui-ci sur une partie de la gamme de couleurs de l'imprimante ;
b) un moyen pour utiliser ledit second ensemble de mises en correspondance de couleurs Pj et un premier ensemble de plans correspondant au premier ensemble de mises en correspondance de couleurs Ao et chaque mise en correspondance dans ledit second ensemble de mises en correspondance de couleurs Pj est défini par des points situés à une intersection de trois plans, les points d'intersection du nombre agrandi de plans définissant un ensemble de points Pi(agrandis) correspondant à un troisième ensemble de mises en correspondance de couleurs Pj(agrandis)
c) un moyen pour générer une matrice rectangulaire remplie de mises en correspondance de couleurs définies par l'ensemble de mises en correspondance de couleurs A1, à partir de la mise en correspondance du premier ensemble de couleurs A0, desdites mises en correspondance du second ensemble de couleurs Pj et dudit troisième ensemble de mises en correspondance de couleurs Pj(agrandis) ;
d) un moyen pour générer un nouvel étalonnage pour ledit système d'impression dérivé desdites mises en correspondance de couleurs A1.
a) direction d'un ensemble de corrections des signaux d'imprimante vers ledit système d'impression pour imprimer un ensemble de pastilles couleur avec des colorants sur un support correspondant à une région d'espace couleur de non linéarité ;
b) mesure de la réponse colorimétrique de ladite imprimante dans ladite région de l'espace couleur de non-linéarité à partir de dudit ensemble de pastilles couleur et de génération de signaux de réponse colorimétrique qui en sont représentatifs ;
c) génération d'un second ensemble de mises en correspondance de couleurs Pj, mettant en correspondance le jeu de correction de signaux d'imprimante avec de signaux de réponse colorimétriques, ledit second ensemble de mises en correspondance de couleurs Pj étant plus petit que le premier ensemble de mises en correspondance de couleurs A0 et chevauchant celui-ci sur une partie de la gamme de l'imprimante ;
d) utilisation dudit second ensemble de mises en correspondance de couleurs Pi et d'un premier ensemble de plans correspondant au premier ensemble de mises en correspondance de couleurs A0 identifiant un ensemble agrandi de plans dans lequel chaque mise en correspondance dans le premier ensemble de mises en correspondance de couleurs A0 et chaque mise en correspondance dans ledit second ensemble de mises en correspondance de couleurs Pj sont définies par des points situés à une intersection de trois plans, les points d'intersection du nombre agrandi de plans définissant un ensemble de points Pj(agrandis) correspondant à un troisième ensemble de mises en correspondance de points Pj(agrandis) ;
e) génération d'une matrice rectangulaire remplie de mises en correspondance de couleurs définies par un ensemble de mises en correspondance de couleurs A1, dérivé de la première mise en correspondance d'un ensemble de couleurs A0, lesdites secondes mises en correspondance d'ensembles de couleurs Pj et ledit troisième ensemble de mises en correspondance de couleurs Pj(agrandi) ;
f) application d'une opération d'interpolation inverse audit ensemble de mises en correspondance de couleurs A1 pour dériver une nouvelle mise en correspondance de signaux de réponse colorimétrique avec des signaux d'imprimante, adressables par lesdits signaux de réponse colorimétrique, avec pour effet de générer un nouvel étalonnage pour ledit système d'impression.